Answer:
The government forbids marihuana essentially for two reasons:
- It believes that marihuana is a harmful drug, that can lead to addiction, and worse, can lead to the use of even harder drugs like cocaine or heroine.
- It cannot be fully convinced by advocates for legalization (unconvincing advocay). Besides, many people are prejudiced against marihuana, and opposing legalization results in political popularity.
The arguments above, while not fully invalid, are not strong enough to continue the support of marihuana ilegalization. While marihuana can be harmful, and addictive, it is not much more harmful than other legal drugs such as alcohol or tobacco. Besides, it does have many medicinal uses, and finally, several states have decided to legalize marihuana and the experience has been largely positive (for example, Colorado).